Random access point access unit in scalable video coding

ABSTRACT

Methods, devices and systems for configuring different access units in scalable video coding are described. In one example aspect, a method of video processing include performing a conversion between a video comprising one or more pictures in one or more video layers and a bitstream of a video, wherein the bitstream comprises a coded video sequence that includes one or more access units, and wherein the bitstream further comprises a first syntax element indicating whether an access unit includes a picture for each video layer making up the coded video sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/US2021/022400, filed on Mar. 15, 2021 which claims the priorityto and benefits of U.S. Provisional Patent Application No. 62/990,387filed on Mar. 16, 2020. All the aforementioned patent applications arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to image and video coding and decoding.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The present document discloses techniques, which include configuringdifferent access units in scalable video coding, that can be used byvideo encoders and decoders for processing coded representation of videousing control information useful for decoding of the codedrepresentation.

In one example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more pictures in one or more video layers and a bitstream of a video,wherein the bitstream comprises a coded video sequence that includes oneor more access units, and wherein the bitstream further comprises afirst syntax element indicating whether an access unit includes apicture for each video layer making up the coded video sequence.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each picture in a given access unitcarries a layer identifier that is equal to a layer identifier of afirst access unit of the coded video sequence comprising the one or morevideo layers.

In yet another example aspect, a video processing method is disclosed.The method includes performing, a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream furthercomprises a first syntax element indicative of an access unit of the oneor more access units starting a new coded video sequence.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that a coded video sequence start accessunit, which starts a new coded video sequence, comprises a picture foreach video layer specified in a video parameter set.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that a given access unit is identified as acoded video sequence start access unit based on the given access unitbeing a first access unit in the bitstream or an access unit previous tothe given access unit comprising end of sequence network abstractionlayer units.

In yet another example aspect, a video processing method is disclosed.The method includes performing, based on a rule, a conversion between avideo comprising one or more pictures in one or more video layers and abitstream of the video, wherein the bitstream comprises a coded videosequence that includes one or more access units, and wherein the rulespecifies that side information is used to indicate whether an accessunit of the one or more access units is a coded video sequence startaccess unit.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each access unit of the one or moreaccess units that is a gradual decoding refresh access unit includesexactly one picture for each video layer present in the coded videosequence.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each access unit of the one or moreaccess units that is an intra random access points access unit includesexactly one picture for each video layer present in the coded videosequence.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a computer readable medium having codestored thereon is disclose. The code embodies one of the methodsdescribed herein in the form of processor-executable code.

These, and other, features are described throughout the presentdocument.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example video processing system inwhich various techniques disclosed herein may be implemented.

FIG. 2 is a block diagram of an example hardware platform used for videoprocessing.

FIG. 3 is a block diagram that illustrates an example video codingsystem that can implement some embodiments of the present disclosure.

FIG. 4 is a block diagram that illustrates an example of an encoder thatcan implement some embodiments of the present disclosure.

FIG. 5 is a block diagram that illustrates an example of a decoder thatcan implement some embodiments of the present disclosure.

FIGS. 6-13 show flowcharts for example methods of video processing.

DETAILED DESCRIPTION

Section headings are used in the present document for ease ofunderstanding and do not limit the applicability of techniques andembodiments disclosed in each section only to that section. Furthermore,H.266 terminology is used in some description only for ease ofunderstanding and not for limiting scope of the disclosed techniques. Assuch, the techniques described herein are applicable to other videocodec protocols and designs also.

1. INITIAL DISCUSSION

This document is related to video coding technologies. Specifically, itis about specifying and signaling of random access point access unit inscalable video coding, wherein a video bitstream can contains more thanone layer. The ideas may be applied individually or in variouscombination, to any video coding standard or non-standard video codecthat supports multi-layer video coding, e.g., the being-developedVersatile Video Coding (VVC).

2. ABBREVIATIONS

APS Adaptation Parameter Set

AU Access Unit

AUD Access Unit Delimiter

AVC Advanced Video Coding

CLVS Coded Layer Video Sequence

CPB Coded Picture Buffer

CRA Clean Random Access

CTU Coding Tree Unit

CVS Coded Video Sequence

DCI Decoding Capability Information

DPB Decoded Picture Buffer

EOB End Of Bitstream

EOS End Of Sequence

GDR Gradual Decoding Refresh

HEVC High Efficiency Video Coding

HRD Hypothetical Reference Decoder

IDR Instantaneous Decoding Refresh

JEM Joint Exploration Model

MCTS Motion-Constrained Tile Sets

NAL Network Abstraction Layer

OLS Output Layer Set

PH Picture Header

PPS Picture Parameter Set

PTL Profile, Tier and Level

PU Picture Unit

RAP Random Access Point

RB SP Raw Byte Sequence Payload

SEI Supplemental Enhancement Information

SPS Sequence Parameter Set

SVC Scalable Video Coding

VCL Video Coding Layer

VPS Video Parameter Set

VTM VVC Test Model

VUI Video Usability Information

VVC Versatile Video Coding

3. VIDEO CODING INTRODUCTION

Video coding standards have evolved primarily through the development ofthe well-known International Telecommunication Union-TelecommunicationStandardization Sector (ITU-T) and International Organization forStandardization (ISO)/International Electrotechnical Commission (IEC)standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MovingPicture Experts Group (MPEG)-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond High EfficiencyVideo Coding (HEVC), the Joint Video Exploration Team (JVET) was foundedby Video Coding Experts Group (VCEG) and MPEG jointly in 2015. Sincethen, many new methods have been adopted by JVET and put into thereference software named Joint Exploration Model (JEM). The JVET meetingis concurrently held once every quarter, and the new coding standard istargeting at 50% bitrate reduction as compared to HEVC. The new videocoding standard was officially named as Versatile Video Coding (VVC) inthe April 2018 JVET meeting, and the first version of VVC test model(VTM) was released at that time. As there are continuous effortcontributing to VVC standardization, new coding techniques are beingadopted to the VVC standard in every JVET meeting. The VVC working draftand test model VTM are then updated after every meeting. The VVC projectis now aiming for technical completion, Final Draft InternationalStandard (FDIS), at the July 2020 meeting.

3.1. Random Access and its Supports in HEVC and VVC

Random access refers to starting access and decoding of a bitstream froma picture that is not the first picture of the bitstream in decodingorder. To support tuning in and channel switching in broadcast/multicastand multiparty video conferencing, seeking in local playback andstreaming, as well as stream adaptation in streaming, the bitstreamneeds to include frequent random access points, which are typicallyintra coded pictures but may also be inter-coded pictures (e.g., in thecase of gradual decoding refresh).

HEVC includes signaling of intra random access points (TRAP) pictures inthe network abstraction layer (NAL) unit header, through NAL unit types.Three types of TRAP pictures are supported, namely instantaneous decoderrefresh (IDR), clean random access (CRA), and broken link access (BLA)pictures. IDR pictures are constraining the inter-picture predictionstructure to not reference any picture before the currentgroup-of-pictures (GOP), conventionally referred to as closed-GOP randomaccess points. CRA pictures are less restrictive by allowing certainpictures to reference pictures before the current GOP, all of which arediscarded in case of a random access. CRA pictures are conventionallyreferred to as open-GOP random access points. BLA pictures usuallyoriginate from splicing of two bitstreams or part thereof at a CRApicture, e.g., during stream switching. To enable better systems usageof TRAP pictures, altogether six different NAL units are defined tosignal the properties of the TRAP pictures, which can be used to bettermatch the stream access point types as defined in the ISO base mediafile format (ISOBMFF), which are utilized for random access support indynamic adaptive streaming over HTTP (DASH).

VVC supports three types of TRAP pictures, two types of IDR pictures(one type with or the other type without associated random accessdecodable leading (RADL) pictures) and one type of CRA picture. Theseare basically the same as in HEVC. The BLA picture types in HEVC are notincluded in VVC, mainly due to two reasons: i) The basic functionalityof BLA pictures can be realized by CRA pictures plus the end of sequenceNAL unit, the presence of which indicates that the subsequent picturestarts a new coded video sequence (CVS) in a single-layer bitstream. Ii)There was a desire in specifying less NAL unit types than HEVC duringthe development of VVC, as indicated by the use of five instead of sixbits for the NAL unit type field in the NAL unit header.

Another key difference in random access support between VVC and HEVC isthe support of gradual decoding refresh (GDR) in a more normative mannerin VVC. In GDR, the decoding of a bitstream can start from aninter-coded picture and although at the beginning not the entire pictureregion can be correctly decoded but after a number of pictures theentire picture region would be correct. AVC and HEVC also support GDR,using the recovery point supplemental enhancement information (SEI)message for signaling of GDR random access points and the recoverypoints. In VVC, a new NAL unit type is specified for indication of GDRpictures and the recovery point is signaled in the picture header syntaxstructure. A CVS and a bitstream are allowed to start with a GDRpicture. This means that it is allowed for an entire bitstream tocontain only inter-coded pictures without a single intra-coded picture.The main benefit of specifying GDR support this way is to provide aconforming behavior for GDR. GDR enables encoders to smooth the bit rateof a bitstream by distributing intra-coded slices or blocks in multiplepictures as opposed intra coding entire pictures, thus allowingsignificant end-to-end delay reduction, which is considered moreimportant nowadays than before as ultralow delay applications likewireless display, online gaming, drone based applications become morepopular.

Another GDR related feature in VVC is the virtual boundary signaling.The boundary between the refreshed region (i.e., the correctly decodedregion) and the unrefreshed region at a picture between a GDR pictureand its recovery point can be signaled as a virtual boundary, and whensignaled, in-loop filtering across the boundary would not be applied,thus a decoding mismatch for some samples at or near the boundary wouldnot occur. This can be useful when the application determines to displaythe correctly decoded regions during the GDR process.

TRAP pictures and GDR pictures can be collectively referred to as randomaccess point (RAP) pictures.

3.2. Scalable Video Coding (SVC) in General and in VVC

Scalable video coding (SVC, sometimes also just referred to asscalability in video coding) refers to video coding in which a baselayer (BL), sometimes referred to as a reference layer (RL), and one ormore scalable enhancement layers (Els) are used. In SVC, the base layercan carry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise (SNR) levels.Enhancement layers may be defined relative to a previously encodedlayer. For example, a bottom layer may serve as a BL, while a top layermay serve as an EL. Middle layers may serve as either Els or RLs, orboth. For example, a middle layer (e.g., a layer that is neither thelowest layer nor the highest layer) may be an EL for the layers belowthe middle layer, such as the base layer or any intervening enhancementlayers, and at the same time serve as a RL for one or more enhancementlayers above the middle layer. Similarly, in the Multiview or 3Dextension of the HEVC standard, there may be multiple views, andinformation of one view may be utilized to code (e.g., encode or decode)the information of another view (e.g., motion estimation, motion vectorprediction and/or other redundancies).

In SVC, the parameters used by the encoder or the decoder are groupedinto parameter sets based on the coding level (e.g., video-level,sequence-level, picture-level, slice level, etc.) in which they may beutilized. For example, parameters that may be utilized by one or morecoded video sequences of different layers in the bitstream may beincluded in a video parameter set (VPS), and parameters that areutilized by one or more pictures in a coded video sequence may beincluded in a sequence parameter set (SPS). Similarly, parameters thatare utilized by one or more slices in a picture may be included in apicture parameter set (PPS), and other parameters that are specific to asingle slice may be included in a slice header. Similarly, theindication of which parameter set(s) a particular layer is using at agiven time may be provided at various coding levels.

Thanks to the support of reference picture resampling (RPR) in VVC,support of a bitstream containing multiple layers, e.g., two layers withstandard definition (SD) and high definition (HD) resolutions in VVC canbe designed without the need any additional signal-processing-levelcoding tool, as upsampling needed for spatial scalability support canjust use the RPR upsampling filter. Nevertheless, high-level syntaxchanges (compared to not supporting scalability) are needed forscalability support. Scalability support is specified in VVC version 1.Different from the scalability supports in any earlier video codingstandards, including in extensions of AVC and HEVC, the design of VVCscalability has been made friendly to single-layer decoder designs asmuch as possible. The decoding capability for multi-layer bitstreams arespecified in a manner as if there were only a single layer in thebitstream. E.g., the decoding capability, such as decoded picture buffer(DPB) size, is specified in a manner that is independent of the numberof layers in the bitstream to be decoded. Basically, a decoder designedfor single-layer bitstreams does not need much change to be able todecode multi-layer bitstreams. Compared to the designs of multi-layerextensions of AVC and HEVC, the HLS aspects have been significantlysimplified at the sacrifice of some flexibilities. For example, an IRAPaccess unit (AU) is required to contain a picture for each of the layerspresent in the CVS.

3.3. Parameter Sets

AVC, HEVC, and VVC specify parameter sets. The types of parameter setsinclude sequence parameter set (SPS), picture parameter set (PPS),adaptation parameter set (APS), and video parameter set (VPS). SPS andPPS are supported in all of AVC, HEVC, and VVC. VPS was introduced sinceHEVC and is included in both HEVC and VVC. APS was not included in AVCor HEVC but is included in the latest VVC draft text.

SPS was designed to carry sequence-level header information, and PPS wasdesigned to carry infrequently changing picture-level headerinformation. With SPS and PPS, infrequently changing information neednot to be repeated for each sequence or picture, hence redundantsignaled of this information can be avoided. Furthermore, the use of SPSand PPS enables out-of-band transmission of the important headerinformation, thus not only avoiding the need for redundant transmissionsbut also improving error resilience.

VPS was introduced for carrying sequence-level header information thatis common for all layers in multi-layer bitstreams.

APS was introduced for carrying such picture-level or slice-levelinformation that needs quite some bits to code, can be shared bymultiple pictures, and in a sequence there can be quite many differentvariations.

3.4. Related Definitions in in VVC

Related definitions in the latest VVC text (in JVET-Q2001-Ve/v15) are asfollows.

-   -   Associated IRAP picture (of a particular picture): The previous        IRAP picture in decoding order (when present) having the same        value of nuh_layer_id as the particular picture.    -   Coded video sequence (CVS): A sequence of Aus that consists, in        decoding order, of a CVS start (CUSS) AU, followed by zero or        more Aus that are not CVSS Aus, including all subsequent Aus up        to but not including any subsequent AU that is a CVSS AU.    -   Coded video sequence start (CVSS) AU: An AU in which there is a        prediction unit (PU) for each layer in the CVS and the coded        picture in each PU is a coded layer video sequence (CLVS) start        (CLVSS) picture.    -   Gradual decoding refresh (GDR) AU: An AU in which the coded        picture in each present PU is a GDR picture.    -   Gradual decoding refresh (GDR) PU: A PU in which the coded        picture is a GDR picture.    -   Gradual decoding refresh (GDR) picture: A picture for which each        VCL NAL unit has nal_unit_type equal to GDR_NUT.    -   Intra random access point (IRAP) AU: An AU in which there is a        PU for each layer in the CVS and the coded picture in each PU is        an IRAP picture.    -   Intra random access point (IRAP) picture: A coded picture for        which all VCL NAL units have the same value of nal_unit_type in        the range of IDR_W_RADL to CRA_NUT, inclusive.

3.5. VPS Syntax and Semantics in VVC

VVC supports scalability, also known as scalable video coding, whereinmultiple layers can be encoded in one coded video bitstream.

In the latest VVC text (in JVET-Q2001-Ve/v15), the scalabilityinformation is signaled in the VPS, for which the syntax and semanticsare as follows.

7.3.2.2 Video parameter set syntax

video_parameter_set_rbsp( ) { Descriptor  vps_video_parameter_set_idu(4)  vps_max_layers_minus1 u(6)  vps_max_sublayers_minus1 u(3)  if(vps_max_layers_minus1 > 0 && vps_max_sublayers_minus1 > 0 )  vps_all_layers_same_num_sublayers_flag u(1)  if(vps_max_layers_minus1 > 0 )   vps_all_independent_layers_flag u(1)  for(I = 0; I <= vps_max_layers_minus1; i++ ) {   vps_layer_id[ I ] u(6)  if( I > 0 && !vps_all_independent_layers_flag ) {   vps_independent_layer_flag[ I ] u(1)    if(!vps_independent_layer_flag[ I ] ) {     for( j = 0; j < I; j++ )      vps_direct_ref_layer_flag[ I ][ j ] u(1)    max_tid_ref_present_flag[ I ] u(1)     if( max_tid_ref_present_flag[I ])       max_tid_il_ref_pics_plus1[ I ] u(3)    }   }  }  if(vps_max_layers_minus1 > 0 ) {   if( vps_all_independent_layers_flag )   each_layer_is_an_ols_flag u(1)   if( !each_layer_is_an_ols_flag ) {   if( !vps_all_independent_layers_flag )     ols_mode_idc u(2)    if(ols_mode_idc = = 2 ) {     num_output_layer_sets_minus1 u(8)     for( I= 1; I <= num_output_layer_sets_minus1; I ++)      for( j = 0; j <=vps_max_layers_minus1; j++ )        ols_output_layer_flag[ I ][ j ] u(1)   }   }  }  vps_num_ptls_minus1 u(8)  for( I = 0; I <=vps_num_ptls_minus1; i++ ) {   if( I > 0 )    pt_present_flag[ I ] u(1)  if( vps_max_sublayers_minus1 > 0 &&!vps_all_layers_same_num_sublayers_flag )    ptl_max_temporal_id[ I ]u(3)  }  while( !byte_aligned( ) )   vps_ptl_alignment_zero_bit /* equalto 0 */ f(1)  for( I = 0; I <= vps_num_ptls_minus1; i++ )  profile_tier_level( pt_present flag[ I ], ptl_max_temporal_id[ I ] ) for( I = 0; I < TotalNumOlss; i++ )   if( vps_num_ptls_minus1 > 0 )   ols_ptl_idx[ I ] u(8)  if( !vps_all_independent_layers_flag )  vps_num_dpb_params ue(v)  if( vps_num_dpb_params > 0 &&vps_max_sublayers_minus1 > 0 )   vps_sublayer_dpb_params_present_flagu(1)  for( I = 0; I < vps_num_dpb_params; i++ ) {   if(vps_max_sublayers_minus1 > 0 && !vps_all_layers_same_num_sublayers_flag)    dpb_max_temporal_id[ I ] u(3)   dpb_parameters(dpb_max_temporal_id[ I ], vps_sublayer_dpb_params_present_flag )  } for( I = 0; I < TotalNumOlss; i++ ) {   if( NumLayersInOls[ I ] > l ) {   ols_dpb_pic_width[ I ] ue(v)    ols_dpb_pic_height[ I ] ue(v)    if(vps_num_dpb_params > 1 )     ols_dpb_params_idx[ I ] ue(v)   }  }  if(!each_layer_is_an_ols_flag )   vps_general_hrd_params_present_flag u(1) if( vps_general_hrd_params_present_flag ) {   general_hrd_parameters( )  if( vps_max_sublayers_minus1 > 0 )   vps_sublayer_cpb_params_present_flag u(1)   num_ols_hrd_params_minus1ue(v)   for( I = 0; I <= num_ols_hrd_params_minus1; i++ ) {    if(vps_max_sublayers_minus1 > 0 && !vps_all_layers_same_num_sublayers_flag)     hrd_max_tid[ I ] u(3)    firstSubLayer =vps_sublayer_cpb_params_present_flag ? 0 : hrd_max_tid[ I ]   ols_hrd_parameters( firstSubLayer, hrd_max_tid[ I ] )   }   if(num_ols_hrd_params_minus1 + 1 != TotalNumOlss &&    num_ols_hrd_params_minus1 > 0 )    for( I = 1; I < TotalNumOlss; i++)     if( NumLayersInOls[ I ] > 1 )      ols_hrd_idx[ I ] ue(v)  } vps_extension_flag u(1)  if( vps_extension_flag )   while(more_rbsp_data( ) )    vps_extension_data_flag u(1)  rbsp_trailing_bits() }7.4.3.2 Video Parameter Set RBSP SemanticsA VPS raw byte sequence payload (RBSP) shall be available to thedecoding process prior to it being referenced, included in at least oneAU with TemporalId equal to 0 or provided through external means. AllVPS NAL units with a particular value of vps_video_parameter_set_id in aCVS shall have the same content.Vps_video_parameter_set_id provides an identifier for the VPS forreference by other syntax elements. The value ofvps_video_parameter_set_id shall be greater than 0.Vps_max_layers_minus1 plus 1 specifies the maximum allowed number oflayers in each CVS referring to the VPS.Vps_max_sublayers_minus1 plus 1 specifies the maximum number of temporalsublayers that may be present in a layer in each CVS referring to theVPS. The value of vps_max_sublayers_minus1 shall be in the range of 0 to6, inclusive.Vps_all_layers_same_num_sublayers_flag equal to 1 specifies that thenumber of temporal sublayers is the same for all the layers in each CVSreferring to the VPS. Vps_all_layers_same_num_sublayers_flag equal to 0specifies that the layers in each CVS referring to the VPS may or maynot have the same number of temporal sublayers. When not present, thevalue of vps_all_layers_same_num_sublayers_flag is inferred to be equalto 1.Vps_all_independent_layers_flag equal to 1 specifies that all layers inthe CVS are independently coded without using inter-layer prediction.Vps_all_independent_layers_flag equal to 0 specifies that one or more ofthe layers in the CVS may use inter-layer prediction. When not present,the value of vps_all_independent_layers_flag is inferred to be equal to1.Vps_layer_id[I] specifies the nuh_layer_id value of the i-th layer. Forany two non-negative integer values of m and n, when m is less than n,the value of vps_layer_id[m] shall be less than vps_layer_id[n].Vps_independent_layer_flag[I] equal to 1 specifies that the layer withindex I does not use inter-layer prediction.Vps_independent_layer_flag[I] equal to 0 specifies that the layer withindex I may use inter-layer prediction and the syntax elementsvps_direct_ref_layer_flag[I][j] for j in the range of 0 to I−1,inclusive, are present in VPS. When not present, the value ofvps_independent_layer_flag[I] is inferred to be equal to 1.Vps_direct_ref_layer_flag[I][j] equal to 0 specifies that the layer withindex j is not a direct reference layer for the layer with index i.vps_direct_ref_layer_flag [I][j] equal to 1 specifies that the layerwith index j is a direct reference layer for the layer with index i.When vps_direct_ref_layer_flag[I][j] is not present for I and j in therange of 0 to vps_max_layers_minus1, inclusive, it is inferred to beequal to 0. When vps_independent_layer_flag[I] is equal to 0, thereshall be at least one value of j in the range of 0 to I−1, inclusive,such that the value of vps_direct_ref_layer_flag[I][j] is equal to 1.The variables NumDirectRefLayers[I], DirectRefLayerIdx[I][d],NumRefLayers[I], RefLayerIdx[I][r], and LayerUsedAsRefLayerFlag[j] arederived as follows:

for( I = 0; I <= vps_max_layers_minus1; i++ ) {  for( j = 0; j <=vps_max_layers_minus1; j++ ) {   dependencyFlag[ I ][ j ] =vps_direct_ref_layer_flag[ I ][ j ]   for( k = 0; k < I; k++ )    if(vps_direct_ref_layer_flag[ I ][ k ] && dependencyFlag[ k ][ j ] )    dependencyFlag[ I ][ j ] = 1  }  LayerUsedAsRefLayerFlag[ I ] = 0 }for( I = 0; I <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r =0; j <= vps_max_layers_minus1; j++ ) {     (37)   if(vps_direct_ref_layer_flag[ I ][ j ] ) {    DirectRefLayerIdx[ I ][ d++ ]= j    LayerUsedAsRefLayerFlag[ j ] = 1   }   if( dependencyFlag[ I ][ j] )    RefLayerIdx[ I ][ r++ ] = j  }  NumDirectRefLayers[ I ] = d NumRefLayers[ I ] = r }The variable GeneralLayerIdx[I], specifying the layer index of the layerwith nuh_layer_id equal to vps_layer_id[I], is derived as follows:for(I=0;I<=vps_max_layers_minus1;i++)GeneralLayerIdx[vps_layer_id[I]]=i  (38)For any two different values of I and j, both in the range of 0 tovps_max_layers_minus1, inclusive, when dependencyFlag[I][j] equal to 1,it is a requirement of bitstream conformance that the values ofchroma_format_idc and bit_depth_minus8 that apply to the i-th layershall be equal to the values of chroma_format_idc and bit_depth_minus8,respectively, that apply to the j-th layer.Max_tid_ref_present_flag[I] equal to 1 specifies that the syntax elementmax_tid_il_ref_pics_plus1[I] is present. Max_tid_ref_present_flag[I]equal to 0 specifies that the syntax elementmax_tid_il_ref_pics_plus1[I] is not present.Max_tid_il_ref_pics_plus1[I] equal to 0 specifies that inter-layerprediction is not used by non-IRAP pictures of the i-th layer.Max_tid_il_ref_pics_plus1[I] greater than 0 specifies that, for decodingpictures of the i-th layer, no picture with TemporalId greater thanmax_tid_il_ref_pics_plus1[I]−1 is used as an inter layer referencepicture (ILRP). When not present, the value ofmax_tid_il_ref_pics_plus1[I] is inferred to be equal to 7.Each_layer_is_an_ols_flag equal to 1 specifies that each output layerset (OLS) contains only one layer and each layer itself in a CVSreferring to the VPS is an OLS with the single included layer being theonly output layer. Each_layer_is_an_ols_flag equal to 0 that an OLS maycontain more than one layer. If vps_max_layers_minus1 is equal to 0, thevalue of each_layer_is_an_ols_flag is inferred to be equal to 1.Otherwise, when vps_all_independent_layers_flag is equal to 0, the valueof each_layer_is_an_ols_flag is inferred to be equal to 0.Ols_mode_idc equal to 0 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLSincludes the layers with layer indices from 0 to I, inclusive, and foreach OLS only the highest layer in the OLS is output.Ols_mode_idc equal to 1 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLSincludes the layers with layer indices from 0 to I, inclusive, and foreach OLS all layers in the OLS are output.Ols_mode_idc equal to 2 specifies that the total number of OLSsspecified by the VPS is explicitly signalled and for each OLS the outputlayers are explicitly signalled and other layers are the layers that aredirect or indirect reference layers of the output layers of the OLS.The value of ols_mode_idc shall be in the range of 0 to 2, inclusive.The value 3 of ols_mode_idc is reserved for future use by ITU-T|ISO/IEC.When vps_all_independent_layers_flag is equal to 1 andeach_layer_is_an_ols_flag is equal to 0, the value of ols_mode_idc isinferred to be equal to 2.Num_output_layer_sets_minus1 plus 1 specifies the total number of OLSsspecified by the VPS when ols_mode_idc is equal to 2.The variable TotalNumOlss, specifying the total number of OLSs specifiedby the VPS, is derived as follows:

if( vps_max_layers_minus1 = = 0 )  TotalNumOlss = 1 else if(each_layer_is_an_ols_flag | | ols_mode_idc = = 0 | | ols_mode_idc = = 1)  TotalNumOlss = vps_max_layers_minus1 + 1         (39) else if(ols_mode_idc = = 2 )  TotalNumOlss = num_output_layer_sets_minus1 + 1ols_output_layer_flag[I][j] equal to 1 specifies that the layer withnuh_layer_id equal to vps_layer_id[j] is an output layer of the i-th OLSwhen ols_mode_idc is equal to 2.Ols_output_layer_flag[I][j] equal to 0 specifies that the layer withnuh_layer_id equal to vps_layer_id[j] is not an output layer of the i-thOLS when ols_mode_idc is equal to 2.The variable NumOutputLayersInOls[I], specifying the number of outputlayers in the i-th OLS, the variable NumSubLayersInLayerInOLS[I][j],specifying the number of sublayers in the j-th layer in the i-th OLS,the variable OutputLayerIdInOls[I][j], specifying the nuh_layer_id valueof the j-th output layer in the i-th OLS, and the variableLayerUsedAsOutputLayerFlag[k], specifying whether the k-th layer is usedas an output layer in at least one OLS, are derived as follows:

NumOutputLayersInOls[ 0 ] = 1 OutputLayerIdInOls[ 0 ][ 0 ] =vps_layer_id[ 0 ] NumSubLayersInLayerInOLS[ 0 ][ 0 ] =vps_max_sub_layers_minus1 + 1 LayerUsedAsOutputLayerFlag[ 0 ] = 1 for( I= 1, I <= vps_max_layers_minus1; i++ ) {  if( each_layer_is_an_ols_flag| | ols_mode_idc < 2 )   LayerUsedAsOutputLayerFlag[ I ] = 1  else /*(!each_layer_is_an_ols_flag && ols_mode_idc = = 2 ) */  LayerUsedAsOutputLayerFlag[ I ] = 0 } for( I = 1; I < TotalNumOlss;i++ )  if( each_layer_is_an_ols_flag | | ols_mode_idc = = 0 ) {  NumOutputLayersInOls[ I ] = 1   OutputLayerIdInOls[ I ][ 0 ] =vps_layer_id[ I ]   for( j = 0; j < I && ( ols_mode_idc = = 0 ); j++ )   NumSubLayersInLayerInOLS[ I ][ j ] = max_tid_il_ref_pics_plus1[ I ]  NumSubLayersInLayerInOLS[ I ][ I ] = vps_max_sub_layers_minus1 + 1  }else if( ols_mode_idc = = 1 ) {   NumOutputLayersInOls[ I ] = I + 1  for( j = 0; j < NumOutputLayersInOls[ I ]; j++ ) {   OutputLayerIdInOls[ I ][ j ] = vps_layer_id[ j ]   NumSubLayersInLayerInOLS[ I ][ j ] = vps_max_sub_layers_minus1 + 1  }  } else if( ols_mode_idc = = 2 ) {   for( j = 0; j <=vps_max_layers_minus1; j++ ) {    layerIncludedInOlsFlag[ I ][ j ] = 0   NumSubLayersInLayerInOLS[ I ][ j ] = 0   }   for( k = 0, j = 0; k <=vps_max_layers_minus1; k++ )       (40)    if( ols_output_layer_flag[ I][ k ] ) {     layerIncludedInOlsFlag[ I ][ k ] = 1    LayerUsedAsOutputLayerFlag[ k ] = 1     OutputLayerIdx[ I ][ j ] = k    OutputLayerIdInOls[ I ][ j++ ] = vps_layer_id[ k ]    NumSubLayersInLayerInOLS[ I ][ j ] = vps_max_sub_layers_minus1 + 1   }   NumOutputLayersInOls[ I ] = j   for( j = 0; j <NumOutputLayersInOls[ I ]; j++ ) {    idx = OutputLayerIdx[ I ][ j ]   for( k = 0; k < NumRefLayers[ idx ]; k++ ) {    layerIncludedInOlsFlag[ I ][ RefLayerIdx[ idx ][ k ] ] = 1     if(NumSubLayersInLayerInOLS[ I ][ RefLayerIdx[ idx ][ k ] ] <      max_tid_il_ref_pics_plus1[ OutputLayerIdInOls[ I ][ j ] ] )     NumSubLayersInLayerInOLS[ I ][ RefLayerIdx[ idx ][ k ] ] =      max_tid_il_ref_pics_plus1[ OutputLayerIdInOls[ I ][ j ] ]    }   } }For each value of I in the range of 0 to vps_max_layers_minus1,inclusive, the values of LayerUsedAsRefLayerFlag[I] andLayerUsedAsOutputLayerFlag[I] shall not be both equal to 0. In otherwords, there shall be no layer that is neither an output layer of atleast one OLS nor a direct reference layer of any other layer.For each OLS, there shall be at least one layer that is an output layer.In other words, for any value of I in the range of 0 to TotalNumOlss−1,inclusive, the value of NumOutputLayersInOls[I] shall be greater than orequal to 1.The variable NumLayersInOls[I], specifying the number of layers in thei-th OLS, and the variable LayerIdInOls[I][j], specifying thenuh_layer_id value of the j-th layer in the i-th OLS, are derived asfollows:

 NumLayersInOls[ 0 ] = 1  LayerIdInOls[ 0 ][ 0 ] = vps_layer_id[ 0 ] for( I = 1; I < TotalNumOlss; i++ ) {   if( each_layer_is_an_ols_flag ){    NumLayersInOls[ I ] = 1    LayerIdInOls[ I ][ 0 ] = vps_layer_id[ I]    (41)   } else if( ols_mode_idc = = 0 | | ols_mode_idc = = 1 ) {   NumLayersInOls[ I ] = I + 1    for( j = 0; j < NumLayersInOls[ I ];j++ )     LayerIdInOls[ I ][ j ] = vps_layer_id[ j ]   } else if(ols_mode_idc = = 2 ) {    for( k = 0, j = 0; k <= vps_max_layers_minus1;k++ )     if( layerIncludedInOlsFlag[ I ][ k ] )      LayerIdInOls[ I ][j++ ] = vps_layer_id[ k ]    NumLayersInOls[ I ] = j   }  } NOTE 1 - The0-th OLS contains only the lowest layer (i.e., the layer withnuh_layer_id equal to vps_layer_id[ 0 ]) and for the 0-th OLS the onlyincluded layer is output.The variable OlsLayerIdx[I][j], specifying the OLS layer index of thelayer with nuh_layer_id equal to LayerIdInOls[I][j], is derived asfollows:

for( I = 0; I < TotalNumOlss; i++ )  for j = 0; j < NumLayersInOls[ I ];j++ )     (42)   OlsLayerIdx[ I ][ LayerIdInOls[ I ][ j ] ] = jThe lowest layer in each OLS shall be an independent layer. In otherwords, for each I in the range of 0 to TotalNumOlss−1, inclusive, thevalue of vps_independent_layer_flag[GeneralLayerIdx[LayerIdInOls[I][0]]]shall be equal to 1.Each layer shall be included in at least one OLS specified by the VPS.In other words, for each layer with a particular value of nuh_layer_idnuhLayerId equal to one of vps_layer_id[k] for k in the range of 0 tovps_max_layers_minus1, inclusive, there shall be at least one pair ofvalues of I and j, where I is in the range of 0 to TotalNumOlss−1,inclusive, and j is in the range of NumLayersInOls[I]−1, inclusive, suchthat the value of LayerIdInOls[I][j] is equal to nuhLayerId.Vps_num_ptls_minus1 plus 1 specifies the number of profile_tier_level( )syntax structures in the VPS. The value of vps_num_ptls_minus1 shall beless than TotalNumOlss.Pt_present_flag[I] equal to 1 specifies that profile, tier, and generalconstraints information are present in the i-th profile_tier_level( )syntax structure in the VPS. Pt_present_flag[I] equal to 0 specifiesthat profile, tier, and general constraints information are not presentin the i-th profile_tier_level( ) syntax structure in the VPS. The valueof pt_present_flag[0] is inferred to be equal to 1. Whenpt_present_flag[I] is equal to 0, the profile, tier, and generalconstraints information for the i-th profile_tier_level( ) syntaxstructure in the VPS are inferred to be the same as that for the(I−1)-th profile_tier_level( ) syntax structure in the VPS.Ptl_max_temporal_id[I] specifies the TemporalId of the highest sublayerrepresentation for which the level information is present in the i-thprofile_tier_level( ) syntax structure in the VPS. The value ofptl_max_temporal_id[I] shall be in the range of 0 tovps_max_sublayers_minus1, inclusive. When vps_max_sublayers_minus1 isequal to 0, the value of ptl_max_temporal_id[I] is inferred to be equalto 0. When vps_max_sublayers_minus1 is greater than 0 andvps_all_layers_same_num_sublayers_flag is equal to 1, the value ofptl_max_temporal_id[I] is inferred to be equal tovps_max_sublayers_minus1.Vps_ptl_alignment_zero_bit shall be equal to 0.Ols_ptl_idx[I] specifies the index, to the list of profile_tier_level( )syntax structures in the VPS, of the profile_tier_level( ) syntaxstructure that applies to the i-th OLS. When present, the value ofols_ptl_idx[I] shall be in the range of 0 to vps_num_ptls_minus1,inclusive. When vps_num_ptls_minus1 is equal to 0, the value ofols_ptl_idx[I] is inferred to be equal to 0.When NumLayersInOls[I] is equal to 1, the profile_tier_level( ) syntaxstructure that applies to the i-th OLS is also present in the SPSreferred to by the layer in the i-th OLS. It is a requirement ofbitstream conformance that, when NumLayersInOls[I] is equal to 1, theprofile_tier_level( ) syntax structures signalled in the VPS and in theSPS for the i-th OLS shall be identical.Vps_num_dpb_params specifies the number of dpb_parameters( ) syntaxstructures in the VPS. The value of vps_num_dpb_params shall be in therange of 0 to 16, inclusive. When not present, the value ofvps_num_dpb_params is inferred to be equal to 0.Vps_sublayer_dpb_params_present_flag is used to control the presence ofmax_dec_pic_buffering_minus1[ ], max_num_reorder_pics[ ], andmax_latency_increase_plus1[ ] syntax elements in the dpb_parameters( )syntax structures in the VPS. When not present,vps_sub_dpb_params_info_present_flag is inferred to be equal to 0.Dpb_max_temporal_id[I] specifies the TemporalId of the highest sublayerrepresentation for which the DPB parameters may be present in the i-thdpb_parameters( ) syntax structure in the VPS. The value ofdpb_max_temporal_id[I] shall be in the range of 0 tovps_max_sublayers_minus1, inclusive. When vps_max_sublayers_minus1 isequal to 0, the value of dpb_max_temporal_id[I] is inferred to be equalto 0. When vps_max_sublayers_minus1 is greater than 0 andvps_all_layers_same_num_sublayers_flag is equal to 1, the value ofdpb_max_temporal_id[I] is inferred to be equal tovps_max_sublayers_minus1.Ols_dpb_pic_width[I] specifies the width, in units of luma samples, ofeach picture storage buffer for the i-th OLS.Ols_dpb_pic_height[I] specifies the height, in units of luma samples, ofeach picture storage buffer for the i-th OLS.Ols_dpb_params_idx[I] specifies the index, to the list ofdpb_parameters( ) syntax structures in the VPS, of the dpb_parameters( )syntax structure that applies to the i-th OLS when NumLayersInOls[I] isgreater than 1. When present, the value of ols_dpb_params_idx[I] shallbe in the range of 0 to vps_num_dpb_params−1, inclusive. Whenols_dpb_params_idx[I] is not present, the value of ols_dpb_params_idx[I]is inferred to be equal to 0.When NumLayersInOls[I] is equal to 1, the dpb_parameters( ) syntaxstructure that applies to the i-th OLS is present in the SPS referred toby the layer in the i-th OLS.Vps_general_hrd_params_present_flag equal to 1 specifies that the VPScontains a general_hrd_parameters( ) syntax structure and otherhypothetical reference decoder (HRD) parameters.Vps_general_hrd_params_present_flag equal to 0 specifies that the VPSdoes not contain a general_hrd_parameters( ) syntax structure or otherHRD parameters. When not present, the value ofvps_general_hrd_params_present_flag is inferred to be equal to 0.When NumLayersInOls[I] is equal to 1, the general_hrd_parameters( )syntax structure and the ols_hrd_parameters( ) syntax structure thatapply to the i-th OLS are present in the SPS referred to by the layer inthe i-th OLS.Vps_sublayer_cpb_params_present_flag equal to 1 specifies that the i-thols_hrd_parameters( ) syntax structure in the VPS contains HRDparameters for the sublayer representations with TemporalId in the rangeof 0 to hrd_max_tid[I], inclusive. Vps_sublayer_cpb_params_present_flagequal to 0 specifies that the i-th ols_hrd_parameters( ) syntaxstructure in the VPS contains HRD parameters for the sublayerrepresentation with TemporalId equal to hrd_max_tid[I] only. Whenvps_max_sublayers_minus1 is equal to 0, the value ofvps_sublayer_cpb_params_present_flag is inferred to be equal to 0.When vps_sublayer_cpb_params_present_flag is equal to 0, the HRDparameters for the sublayer representations with TemporalId in the rangeof 0 to hrd_max_tid[I]−1, inclusive, are inferred to be the same as thatfor the sublayer representation with TemporalId equal to hrd_max_tid[I].These include the HRD parameters starting from thefixed_pic_rate_general_flag[I] syntax element till thesublayer_hrd_parameters(I) syntax structure immediately under thecondition “if(general_vcl_hrd_params_present_flag)” in theols_hrd_parameters syntax structure.Num_ols_hrd_params_minus1 plus 1 specifies the number ofols_hrd_parameters( ) syntax structures present in the VPS whenvps_general_hrd_params_present_flag is equal to 1. The value ofnum_ols_hrd_params_minus1 shall be in the range of 0 to TotalNumOlss−1,inclusive.Hrd_max_tid[I] specifies the TemporalId of the highest sublayerrepresentation for which the HRD parameters are contained in the i-thols_hrd_parameters( ) syntax structure. The value of hrd_max_tid[I]shall be in the range of 0 to vps_max_sublayers_minus1, inclusive. Whenvps_max_sublayers_minus1 is equal to 0, the value of hrd_max_tid[I] isinferred to be equal to 0. When vps_max_sublayers_minus1 is greater than0 and vps_all_layers_same_num_sublayers_flag is equal to 1, the value ofhrd_max_tid[I] is inferred to be equal to vps_max_sublayers_minus1.Ols_hrd_idx[I] specifies the index, to the list of ols_hrd_parameters( )syntax structures in the VPS, of the ols_hrd_parameters( ) syntaxstructure that applies to the i-th OLS when NumLayersInOls[I] is greaterthan 1. The value of ols_hrd_idx[[I] shall be in the range of 0 tonum_ols_hrd_params_minus1, inclusive.When NumLayersInOls[I] is equal to 1, the ols_hrd_parameters( ) syntaxstructure that applies to the i-th OLS is present in the SPS referred toby the layer in the i-th OLS.If the value of num_ols_hrd_param_minus1+1 is equal to TotalNumOlss, thevalue of ols_hrd_idx[I] is inferred to be equal to i. Otherwise, whenNumLayersInOls[I] is greater than 1 and num_ols_hrd_params_minus1 isequal to 0, the value of ols_hrd_idx[[I] is inferred to be equal to 0.Vps_extension_flag equal to 0 specifies that no vps_extension_data_flagsyntax elements are present in the VPS RBSP syntax structure.Vps_extension_flag equal to 1 specifies that there arevps_extension_data_flag syntax elements present in the VPS RBSP syntaxstructure.Vps_extension_data flag may have any value. Its presence and value donot affect decoder conformance to profiles specified in this version ofthis Specification. Decoders conforming to this version of thisSpecification shall ignore all vps_extension_data_flag syntax elements.

3.6. Access Unit Delimiter (AUD) Syntax and Semantics in VVC

In the latest VVC text (in JVET-Q2001-Ve/v15), the AUD syntax andsemantics are as follows.

7.3.2.9 AU Delimiter RBSP Syntax

access_unit_delimiter_rbsp( ) { Descriptor  pictype u(3) rbsp_trailing_bits( ) }7.4.3.9 AU Delimiter RBSP SemanticsThe AU delimiter is used to indicate the start of an AU and the type ofslices present in the coded pictures in the AU containing the AUdelimiter NAL unit. There is no normative decoding process associatedwith the AU delimiter.Pic_type indicates that the slice type values for all slices of thecoded pictures in the AU containing the AU delimiter NAL unit aremembers of the set listed in Table 7 for the given value of pic_type.The value of pic_type shall be equal to 0, 1 or 2 in bitstreamsconforming to this version of this Specification. Other values ofpic_type are reserved for future use by ITU-T|ISO/IEC. Decodersconforming to this version of this Specification shall ignore reservedvalues of pic_type.

TABLE 7 Interpretation of pic_type slice_type values that pic_type maybe present in the AU 0 I 1 P, I 2 B, P, I

3.7. Order of Aus and PUs

In the latest VVC text (in JVET-Q2001-Ve/v15), the specification of thedecoding order of Aus and PUs is as follows.

7.4.2.4.2 Order of Aus and their Association to CVSs

A bitstream consists of one or more CVSs.

A CVS consists of one or more Aus. The order of PUs and theirassociation to Aus are described in clause 7.4.2.4.3.

The first AU of a CVS is a CVSS AU, wherein each present PU is a CLVSSPU, which is either an IRAP PU with NoOutputBeforeRecoveryFlag equal to1 or a GDR PU with NoOutputBeforeRecoveryFlag equal to 1.

Each CVSS AU shall have a PU for each of the layers present in the CVS.

7.4.2.4.3 Order of PUs and their Association to Aus

An AU consists of one or more PUs in increasing order of nuh_layer_id.The order NAL units and coded pictures and their association to PUs aredescribed in clause 7.4.2.4.4.

There can be at most one AUD NAL unit in an AU. When an AUD NAL unit ispresent in an AU, it shall be the first NAL unit of the AU, andconsequently, it is the first NAL unit of the first PU of the AU.

There can be at most one end of bitstream (EOB) NAL unit in an AU. Whenan EOB NAL unit is present in an AU, it shall be the last NAL unit ofthe AU, and consequently, it is the last NAL unit of the last PU of theAU.

A VCL NAL unit is the first VCL NAL unit of an AU (and consequently thePU containing the VCL NAL unit is the first PU of the AU) when the VCLNAL unit is the first VCL NAL unit that follows a picture header (PH)NAL unit and one or more of the following conditions are true:

-   -   The value of nuh_layer_id of the VCL NAL unit is less than the        nuh_layer_id of the previous picture in decoding order.    -   The value of ph_pic_order_cnt_lsb of the VCL NAL unit differs        from the ph_pic_order_cnt_lsb of the previous picture in        decoding order.    -   PicOrderCntVal derived for the VCL NAL unit differs from the        PicOrderCntVal of the previous picture in decoding order.        Let firstVclNalUnitInAu be the first VCL NAL unit of an AU. The        first of any of the following NAL units preceding        firstVclNalUnitInAu and succeeding the last VCL NAL unit        preceding firstVclNalUnitInAu, if any, specifies the start of a        new AU:    -   AUD NAL unit (when present),    -   Decoding Capability Information (DCI) NAL unit (when present),    -   VPS NAL unit (when present),    -   SPS NAL unit (when present),    -   PPS NAL unit (when present),    -   Prefix APS NAL unit (when present),    -   PH NAL unit (when present),    -   Prefix SEI NAL unit (when present),    -   NAL unit with nal_unit_type equal to RSV_NVCL_26 (when present),    -   NAL unit with nal_unit_type in the range of UNSPEC28 . . .        UNSPEC29 (when present).    -   NOTE—The first NAL unit preceding firstVclNalUnitInAu and        succeeding the last VCL NAL unit preceding firstVclNalUnitInAu,        if any, can only be one of the above-listed NAL units.        It is a requirement of bitstream conformance that, when present,        the next PU of a particular layer after a PU that belongs to the        same layer and contains an end of sequence (EOS) NAL unit shall        be a CLVSS PU, which is either an IRAP PU with        NoOutputBeforeRecoveryFlag equal to 1 or a GDR PU with        NoOutputBeforeRecoveryFlag equal to 1.

4. EXAMPLES OF TECHNICAL PROBLEMS SOLVED BY DISCLOSED TECHNICALSOLUTIONS

The existing scalability design in the latest VVC text (inJVET-Q2001-Ve/v15) has the following problems:

-   -   1) A CVSS AU, which starts a new CVS, is required to be complete        (i.e., to have a picture for each of the layers present in the        CVS). However, according to the current design, the decoder is        not able to check whether an AU includes a picture “for each of        the layers present in the CVS” before it receives the last        picture of the CVS, while on the other hand, even the last        picture of the CVS is not easy to be determined because it is        not easy to determine the start of any of CVS except for the        very first CVS of the bitstream. Basically, that means, the        decoder can only figure out the boundaries of CVSs after        receiving the entire bitstream.    -   2) Currently, an IRAP AU may start a new CVS and is required to        be complete (i.e., to have a picture for each of the layers        present in the CVS), while a GDR AU may also start a new CVS but        is NOT required to be complete. This basically disables random        accessing a bitstream starting from a GDR AU that is not        complete in a conforming manner, because usually the starting AU        in random accessing would become a CVSS AU but when such a GDR        AU is incomplete it cannot be a CVSS AU.

5. EXAMPLE EMBODIMENTS AND TECHNIQUES

To solve the above problems, and others, methods as summarized below aredisclosed. The embodiments should be considered as examples to explainthe general concepts and should not be interpreted in a narrow way.Furthermore, these embodiments can be applied individually or combinedin any manner.

Solutions for Solving the First Problem

-   -   1) To solve the first problem, an indication of whether an AU is        complete, in the sense whether it includes a picture for each of        the layers present in the CVS, may be signaled.        -   a. In one example, the indication is signaled only for Aus            that may start a new CVS.            -   i. In one example, furthermore, the indication is                signaled only for Aus for which each picture is an IRAP                or GDR picture.        -   b. In one example, the indication is signaled in the AUD NAL            unit.            -   i. In one example, the indication is signaled by a flag                (e.g., irap_or_gdr_au_flag) in the AUD NAL unit.                -   1. Alternatively, additionally, when                    irap_or_gdr_au_flag is equal to 1, a flag (i.e.,                    named irap_au_flag) may be signalled in the AUD to                    specify whether the AU is an IRAP AU or a GDR AU                    (irap_au_flag equal to 1 specifies that the AU is an                    IRAP AU, and irap_au_flag equal to 0 specifies that                    the AU is a GDR AU). No value of irap_au_flag is                    inferred when it is not present.            -   ii. In one example, furthermore, one and only one AUD                NAL unit is required to be present in each IRAP or GDR                AU when vps_max_layers_minus1 is greater than 0.                -   1. Alternatively, one and only one AUD NAL unit is                    required to be present in each IRAP or GDR AU                    regardless of the value of vps_max_layers_minus1.            -   iii. In one example, the flag equal to 1 specifies that                all slices in the AU have the same NAL unit type in the                range of IDR_W_RADL to GDR_NUT, inclusive. Consequently,                if the NAL unit type is IDR_W_RADL or IDR_N_LP and this                flag is equal to 1, the AU is a CVSS AU. Otherwise (the                NAL unit type is CRA_NUT or GDR_NUT), the AU is a CVSS                AU when the variable NoOutputBeforeRecoveryFlag for each                of the pictures in the AU is equal to 1.        -   c. In one example, furthermore, it is required that each            picture in an AU in a CVS shall have nuh_layer_id equal to            the nuh_layer_id of one of the pictures present in the first            AU of the CVS.        -   d. In one example, the indication is signaled in the NAL            unit header.            -   i. In one example, use a bit in the NAL unit header,                e.g., nuh_reserved_zero_bit, to specify whether the AU                is complete.        -   e. In one example, the indication is signaled in a new NAL            unit.            -   i. In one example, furthermore, the presence of one and                only one of the new NAL unit in each IRAP or GDR AU is                required when vps_max_layers_minus1 is greater than 0.                -   1. In one example, furthermore, when present in an                    AU, the new NAL unit shall precede any NAL unit                    other than the AUD NAL unit, when present, in the AU                    in decoding order.                -   2. Alternatively, the presence of one and only one                    of the new NAL unit in each IRAP or GDR AU is                    required regardless of the value of                    vps_max_layers_minus1.        -   f. In one example, the indication is signaled in an SEI            message.            -   i. In one example, furthermore, the presence of the SEI                message in each IRAP or GDR AU is required when                vps_max_layers_minus1 is greater than 0.                -   1. In one example, furthermore, when present in an                    AU, the SEI NAL unit containing the SEI message                    shall precede any NAL unit other than the AUD NAL                    unit, when present, in the AU in decoding order.                -   2. Alternatively, the presence of the SEI message in                    each IRAP or GDR AU is required regardless of the                    value of vps_max_layers_minus1.    -   2) Alternatively, to solve the first problem, an indication of        whether an AU starts a new CVS may be signaled.        -   a. In one example, the indication is signaled in the AUD NAL            unit.            -   i. In one example, the indication is signaled by a flag                (e.g., irap_or_gdr_au_flag) in the AUD NAL unit.                -   1. Alternatively, additionally, when                    irap_or_gdr_au_flag is equal to 1, a flag (i.e.,                    named irap_au_flag) may be signalled in the AUD to                    specify whether the AU is an IRAP AU or a GDR AU                    (irap_au_flag equal to 1 specifies that the AU is an                    IRAP AU, and irap_au_flag equal to 0 specifies that                    the AU is a GDR AU). No value of irap_au_flag is                    inferred when it is not present.            -   ii. In one example, furthermore, one and only one AUD                NAL unit is required to be present in each CVSS AU when                vps_max_layers_minus1 is greater than 0.                -   1. Alternatively, one and only one AUD NAL unit is                    required to be present in each CVSS AU regardless of                    the value of vps_max_layers_minus1.        -   b. In one example, the indication is signaled in the NAL            unit header.            -   i. In one example, use a bit in the NAL unit header,                e.g., nuh_reserved_zero_bit, to specify whether the AU                is a CVSS AU.        -   c. In one example, the indication is signaled in a new NAL            unit.            -   i. In one example, furthermore, the presence of one and                only one of the new NAL unit in each CVSS AU is required                when vps_max_layers_minus1 is greater than 0.                -   1. In one example, furthermore, when present in an                    AU, the new NAL unit shall precede any NAL unit                    other than the AUD NAL unit, when present, in the AU                    in decoding order.                -   2. Alternatively, the presence of one and only one                    of the new NAL unit in each CVSS AU is required                    regardless of the value of vps_max_layers_minus1.            -   ii. In one example, the presence of the new NAL unit in                an AU specifies that the AU is a CVSS AU.                -   1. Alternatively, a flag is included in the new NAL                    unit to specify whether the AU is a CVSS AU.        -   d. In one example, the indication is signaled in an SEI            message.            -   i. In one example, furthermore, the presence of the SEI                message in each CVSS AU is required when                vps_max_layers_minus1 is greater than 0.                -   1. In one example, furthermore, when present in an                    AU, the SEI NAL unit containing the SEI message                    shall precede any NAL unit other than the AUD NAL                    unit, when present, in the AU in decoding order.    -   2. Alternatively, the presence of the SEI message in each CVSS        AU is required regardless of the value of vps_max_layers_minus1.    -   3) Alternatively, to solve the first problem, a CVSS AU, which        starts a new CVS, is required to have a picture for each of the        layers specified by the VPS. Note that a shortcoming of this        approach is that then the number of layers signaled in the VPS        needs to be precise, and consequently when a layer is removed        from the bitstream the VPS needs to be modified.    -   4) Alternatively, to solve the first problem, when        vps_max_layers_minus1 is greater than 0, mandate the presence of        the EOS NAL unit for each picture in the last AU of each CVS,        and optionally also the presence of the EOB NAL unit in the last        AU of each bitstream. Thus each CVSS AU would be identified by        either being the first AU in the bitstream or the presence of        the EOS NAL units in the previous AU.    -   5) Alternatively, to solve the first problem, an        external-means-determined variable is specified to specify        whether an AU is a CVSS AU.        Solutions for Solving the Second Problem    -   6) To solve the second problem, it is required that each GDR AU        is required to be complete (i.e., to have a picture for each of        the layers present in the CVS). That means, an AU consisting of        GDR pictures but if it is incomplete then it is not a GDR AU,        similarly as currently that an AU consisting of IRAP pictures        but if it is incomplete then it is not an IRAP AU.        -   a. In one example, a GDR AU may be defined as an AU in which            there is a PU for each layer in the CVS and the coded            picture in each present PU is a GDR picture.

6. EMBODIMENTS

Below are some example embodiments for some of the aspects summarizedabove in Section 5, which can be applied to the VVC specification. Thechanged texts are based on the latest VVC text in JVET-Q2001-Ve v15.Most relevant parts that have been added or modified are shown inunderline, bolded and italicized text, and the most relevant removedparts are highlighted in enclosed in bolded double brackets, e.g., [[a]]indicates that “a” has been removed. There are some other changes thatare editorial in nature and thus not highlighted.

6.1. First Embodiment

This embodiment is for items 1, 1.a, 1.a.i, 1.b, 1.b.i, 1.b.ii, 1.b.iii,1.c, 6, and 6a.

3 Definitions

. . .

-   -   gradual decoding refresh (GDR) AU: An AU in which there is a PU        for each layer in the CVS and the coded picture in each present        PU is a GDR picture.        . . .        7.3.2.9 AU Delimiter RBSP Syntax

access_unit_delimiter_rbsp( ) { Descriptor  irap_or_sdr_au_flag u(1) pic_type u(3)  rbsp_trailing_bits( ) }7.4.3.9 AU Delimiter RBSP SemanticsThe AU delimiter is used to indicate the start of an AU, whether the AUis an IRAP or GDRAU, and the type of slices present in the codedpictures in the AU containing the AU delimiter NAL unit. Forsingle-layer bitstreams, there is no normative decoding processassociated with the AU delimiter.Irap_or_gdr_au_flag equal to 1 specifies that the AU containing the AUdelimiter is an IRAP or GDR AU. Irap_or_gdr_au_flag equal to 0 specifiesthat the AU containing the AU delimiter is not an IRAP or GDR AU.. . .7.4.2.4.2 Order of Aus and their Association to CVSsA bitstream consists of one or more CVSs.A CVS consists of one or more Aus. The order of PUs and theirassociation to Aus are described in clause 7.4.2.4.3.The first AU of a CVS is a CVSS AU, wherein each present PU is a CLVSSPU, which is either an IRAP PU with NoOutputBeforeRecoveryFlag equal to1 or a GDR PU with NoOutputBeforeRecoveryFlag equal to 1.Each CVSS AU shall have a PU for each of the layers present in the CVSand each picture in an AU in a CVS shall have nuh_layer_id equal to thenuh_layer_id of one of the pictures present in the first AU of the CVS.7.4.2.4.3 Order of PUs and their Association to AusAn AU consists of one or more PUs in increasing order of nuh_layer_id.The order NAL units and coded pictures and their association to PUs aredescribed in clause 7.4.2.4.4.There can be at most one AUD NAL unit in an AU, and whenvps_max_layers_minus1 is greater than 0, there shall be one and only oneAUD NAL unit in each IRAP or GDR AU.When an AUD NAL unit is present in an AU, it shall be the first NAL unitof the AU, and consequently, it is the first NAL unit of the first PU ofthe AU.There can be at most one EOB NAL unit in an AU. When an EOB NAL unit ispresent in an AU, it shall be the last NAL unit of the AU, andconsequently, it is the last NAL unit of the last PU of the AU.. . .

FIG. 1 is a block diagram showing an example video processing system1000 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 1000. The system 1000 may include input 1002 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 1002 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as wirelessfidelity (Wi-Fi) or cellular interfaces.

The system 1000 may include a coding component 1004 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 1004 may reduce the average bitrate ofvideo from the input 1002 to the output of the coding component 1004 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1004 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1006. The stored or communicated bitstream (or coded)representation of the video received at the input 1002 may be used bythe component 1008 for generating pixel values or displayable video thatis sent to a display interface 1010. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include serial advanced technology attachment (SATA),peripheral component interconnect (PCI), integrated drive electronics(IDE) interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

FIG. 2 is a block diagram of a video processing apparatus 2000. Theapparatus 2000 may be used to implement one or more of the methodsdescribed herein. The apparatus 2000 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 2000 may include one or more processors 2002, one or morememories 2004 and video processing hardware 2006. The processor(s) 2002may be configured to implement one or more methods described in thepresent document. The memory (memories) 2004 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 2006 may be used to implement, inhardware circuitry, some techniques described in the present document.In some embodiments, the hardware 2006 may be partly or entirely in theone or more processors 2002, e.g., a graphics processor.

FIG. 3 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure.

As shown in FIG. 3 , video coding system 100 may include a source device110 and a destination device 120. Source device 110 generates encodedvideo data which may be referred to as a video encoding device.Destination device 120 may decode the encoded video data generated bysource device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114,and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVC) standard and other current and/orfurther standards.

FIG. 4 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 3 .

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 4 , video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a prediction unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, prediction unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performprediction in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 4 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter prediction (CIIP) modein which the prediction is based on an inter prediction signal and anintra prediction signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-prediction.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a fullset of motion information for the current video. Rather, motionestimation unit 204 may signal the motion information of the currentvideo block with reference to the motion information of another videoblock. For example, motion estimation unit 204 may determine that themotion information of the current video block is sufficiently similar tothe motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 5 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 3 .

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 5 , the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 5 , video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (FIG. 4).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 200 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may use some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 304 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 305 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit302 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra predication and also produces decoded videofor presentation on a display device.

FIGS. 6-7 show example methods that can implement the technical solutiondescribed above in, for example, the embodiments shows in FIGS. 1-5 .

FIG. 6 shows a flowchart for an example method 600 of video processing.The method 600 includes, at operation 610, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream further comprising a first syntax element indicatingwhether an AU includes a picture for each video layer making up the CVS.

FIG. 7 shows a flowchart for an example method 700 of video processing.The method 700 includes, at operation 710, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that eachpicture in a given AU carries a layer identifier that is equal to alayer identifier of a first AU of the CVS comprising the one or morevideo layers.

FIG. 8 shows a flowchart for an example method 800 of video processing.The method 800 includes, at operation 810, performing, a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream further comprising a first syntax element indicative of anAU of the one or more AUs starting a new CVS.

FIG. 9 shows a flowchart for an example method 900 of video processing.The method 900 includes, at operation 910, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that a codedvideo sequence start (CVSS) AU, which starts a new CVS, comprises apicture for each video layer specified in a video parameter set (VPS).

FIG. 10 shows a flowchart for an example method 1000 of videoprocessing. The method 1000 includes, at operation 1010, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of the video, the bitstream comprisinga coded video sequence (CVS) that includes one or more access units(AUs), and the bitstream conforming to a format rule that specifies thata given AU is identified as a coded video sequence start (CVSS) AU basedon the given AU being a first AU in the bitstream or an AU previous tothe given AU comprising end of sequence (EOS) network abstraction layer(NAL) units.

FIG. 11 shows a flowchart for an example method 1100 of videoprocessing. The method 1100 includes, at operation 1110, performing,based on a rule, a conversion between a video comprising one or morepictures in one or more video layers and a bitstream of the video, thebitstream comprising a coded video sequence (CVS) that includes one ormore access units (AUs), and the rule specifying that side informationis used to indicate whether an AU of the one or more AUs is a codedvideo sequence start (CVSS) AU.

FIG. 12 shows a flowchart for an example method 1200 of videoprocessing. The method 1200 includes, at operation 1210, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of a video, the bitstream comprising acoded video sequence (CVS) that includes one or more access units (AUs),and the bitstream conforming to a format rule that specifies that eachAU of the one or more AUs that is a gradual decoding refresh AU includesexactly one picture for each video layer present in the CVS.

FIG. 13 shows a flowchart for an example method 1300 of videoprocessing. The method 1300 includes, at operation 1310, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of a video, the bitstream comprising acoded video sequence that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that each AU ofthe one or more AUs that is an intra random access points AU includesexactly one picture for each video layer present in the CVS.

A listing of solutions preferred by some embodiments is provided next.

P1. A video processing method, comprising performing a conversionbetween a video having one or more pictures in one or more video layersand a coded representation representing an encoded version of the video;wherein the coded representation includes one or more access units (AU);wherein the coded representation includes a syntax element if and onlyif an AU is of a type, wherein the syntax element indicates whether theAU includes a picture for each video layer making up a coded videosequence.

P2. The method of solution P1, wherein the type includes all AUs.

P3. The method of solution P1, wherein the type includes AUs that starta new CVS.

P4. The method of solution P1, wherein the syntax element is included inan access unit delimiter network abstraction layer unit.

P5. The method of any of solutions P1 to P4, wherein the syntax elementis included in a network abstraction layer unit header.

P6. The method of any of solutions P1 to P4, wherein the syntax elementis included in new a network abstraction layer unit.

P7. A video processing method, comprising performing a conversionbetween a video having one or more pictures in one or more video layersand a coded representation representing an encoded version of the video;wherein the coded representation includes one or more access units (AU);wherein the coded representation conforms to a format rule thatspecifies that each picture in a given AU carries a layer identifierthat is equal to that of a first AU of a coded video sequence.

P8. A video processing method, comprising performing a conversionbetween a video having one or more pictures in one or more video layersand a coded representation representing an encoded version of the video;wherein the coded representation includes one or more access units (AU);wherein the coded representation includes a syntax element if and onlyif an AU starts a new coded video sequence.

P9. The method of solution P8, wherein the syntax element is included inan access unit delimiter network abstraction layer unit.

P10. The method of any of solutions P8 to P9, wherein the syntax elementis included in a network abstraction layer unit header.

P11. The method of any of solutions P8 to P9, wherein the syntax elementis included as a supplemental enhancement information.

P12. A video processing method, comprising performing a conversionbetween a video having one or more pictures in one or more video layersand a coded representation of the video; wherein the codedrepresentation includes one or more access units (AU); wherein the codedrepresentation conforms to a format rule that specifies that a startingAU for a coded video sequence includes a video picture for each videolayer specified by a video parameter set or that the codedrepresentation implicitly signals the starting AU based on a rule.

P13. A video processing method, comprising performing a conversionbetween a video having one or more pictures in one or more video layersand a coded representation of the video; wherein the codedrepresentation includes one or more access units (AU); wherein the codedrepresentation conforms to a format rule that specifies that each AU oftype gradual decoding refresh (GDR) includes at least a video picturefor each video layer of a coded video sequence.

P14. The method of solution P13, wherein each AU of type GDR furtherincludes a prediction unit for each layer in the CVS and the PUcomprises GDR pictures.

P15. The method of any of solutions P1 to 14, wherein the conversioncomprises encoding the video into the coded representation.

P16. The method of any of solutions P1 to 14, wherein the conversioncomprises decoding the coded representation to generate pixel values ofthe video.

P17. A video decoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions P1 to P16.

P18. A video encoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions P1 to P16.

P19. A computer program product having computer code stored thereon, thecode, when executed by a processor, causes the processor to implement amethod recited in any of solutions P1 to P16.

Another listing of solutions preferred by some embodiments is providednext.

A1. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream further comprises a first syntax element indicatingwhether an access unit includes a picture for each video layer making upthe coded video sequence.

A2. The method of solution A1, wherein the access unit is configured tostart a new coded video sequence.

A3. The method of solution A2, wherein the picture for each video layeris an intra random access point picture or a gradual decoding refreshpicture.

A4. The method of solution A1, wherein the first syntax element isincluded in an access unit delimiter network abstraction layer unit.

A5. The method of solution A4, wherein the first syntax element is aflag indicating whether an access unit containing an access unitdelimiter is an intra random access point access unit or a gradualdecoding refresh access unit.

A6. The method of solution A5, wherein the first syntax element isirap_or_gdr_au_flag.

A7. The method of solution A4, wherein the access unit delimiter networkabstraction layer unit is the only access unit delimiter networkabstraction layer unit present in each intra random access point accessunit or gradual decoding refresh access unit when a second syntaxelement, which is indicative of a number of video layers specified by avideo parameter set, is greater than one.

A8. The method of solution A7, wherein the second syntax elementindicates a maximum allowed number of layers in each coded videosequence that refers to the video parameter set.

A9. The method of solution A1, wherein the first syntax element equalingone is indicative of all slices in the access unit comprising anidentical network abstraction layer unit type in a range of IDR_W_RADLto GDR_NUT, inclusive.

A10. The method of solution A9, wherein the first syntax elementequaling one and the network abstraction layer unit type beingIDR_W_RADL or IDR_N_LP is indicative of the access unit being a codedvideo sequence start access unit.

All. The method of solution A9, wherein a variable for each of thepictures in the access unit equaling one and the network abstractionlayer unit type being CRA_NUT or GDR_NUT is indicative of the accessunit being a coded video sequence start access unit.

A12. The method of solution A11, wherein the variable indicates whetherpictures in a decoded picture buffer prior to a current picture indecoding order are output before the pictures are recovered.

A13. The method of solution A11, wherein the variable isNoOutputBeforeRecoveryFlag.

A14. The method of solution A1, wherein the first syntax element isincluded in a network abstraction layer unit header.

A15. The method of solution A1, wherein the first syntax element isincluded in a new network abstraction layer unit.

A16. The method of solution A15, wherein the new network abstractionlayer unit is the only new network abstraction layer unit present ineach intra random access point access unit or gradual decoding refreshaccess unit when a second syntax element, which is indicative of anumber of video layers specified by a video parameter set, is greaterthan one.

A17. The method of solution A1, wherein the first syntax element isincluded in a supplementary enhancement information message.

A18. The method of solution A17, wherein the supplementary enhancementinformation message is the only supplementary enhancement informationmessage present in each intra random access point access unit or gradualdecoding refresh access unit when a second syntax element, which isindicative of a number of video layers specified by a video parameterset, is greater than zero.

A19. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream conforms to a format rule that specifies that each picturein a given access unit carries a layer identifier that is equal to alayer identifier of a first access unit of the coded video sequencecomprising the one or more video layers.

A20. A method of video processing, comprising performing, a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream further comprises a first syntax element indicative of anaccess unit of the one or more access units starting a new coded videosequence.

A21. The method of solution A20, wherein the first syntax element isincluded in an access unit delimiter network abstraction layer unit.

A22. The method of solution A20, wherein the first syntax element isincluded in a network abstraction layer unit header.

A23. The method of solution A20, wherein the first syntax element isincluded in a new network abstraction layer unit.

A24. The method of solution A20, wherein the first syntax element isincluded in a supplementary enhancement information message.

A25. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream conforms to a format rule that specifies that a codedvideo sequence start access unit, which starts a new coded videosequence, comprises a picture for each video layer specified in a videoparameter set.

A26. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream conforms to a format rule that specifies that a givenaccess unit is identified as a coded video sequence start access unitbased on the given access unit being a first access unit in thebitstream or an access unit previous to the given access unit comprisingend of sequence network abstraction layer units.

A27. A method of video processing, comprising performing, based on arule, a conversion between a video comprising one or more pictures inone or more video layers and a bitstream of the video, wherein thebitstream comprises a coded video sequence that includes one or moreaccess units, and wherein the rule specifies that side information isused to indicate whether an access unit of the one or more access unitsis a coded video sequence start access unit.

A28. The method of any of solutions A1 to A27, wherein the conversioncomprises decoding the video from the bitstream.

A29. The method of any of solutions A1 to A27, wherein the conversioncomprises encoding the video into the bitstream.

A30. A method of storing a bitstream representing a video to acomputer-readable recording medium, comprising generating the bitstreamfrom the video according to a method described in any one or more ofsolutions A1 to A27; and storing the bitstream in the computer-readablerecording medium.

A31. A video processing apparatus comprising a processor configured toimplement a method recited in any one or more of solutions A1 to A30.

A32. A computer-readable medium having instructions stored thereon, theinstructions, when executed, causing a processor to implement a methodrecited in one or more of solutions A1 to A30.

A33. A computer readable medium that stores the bitstream generatedaccording to any one or more of solutions A1 to A30.

A34. A video processing apparatus for storing a bitstream, wherein thevideo processing apparatus is configured to implement a method recitedin any one or more of solutions A1 to A30.

Yet another listing of solutions preferred by some embodiments isprovided next.

B1. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream conforms to a format rule that specifies that each accessunit of the one or more access units that is a gradual decoding refreshaccess unit includes exactly one picture for each video layer present inthe coded video sequence.

B2. The method of solution B1, wherein each access unit that is agradual decoding refresh access unit includes a prediction unit for theeach layer present in the coded video sequence, and wherein theprediction unit for each layer includes a coded picture that is agradual decoding refresh picture.

B3. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, wherein the bitstream comprises acoded video sequence that includes one or more access units, and whereinthe bitstream conforms to a format rule that specifies that each accessunit of the one or more access units that is an intra random accesspoints access unit includes exactly one picture for each video layerpresent in the coded video sequence.

B4. The method of any of solutions B1 to B3, wherein the conversioncomprises decoding the video from the bitstream.

B5. The method of any of solutions B1 to B3, wherein the conversioncomprises encoding the video into the bitstream.

B6. A method of storing a bitstream representing a video to acomputer-readable recording medium, comprising generating the bitstreamfrom the video according to a method described in any one or more ofsolutions B1 to B3; and storing the bitstream in the computer-readablerecording medium.

B7. A video processing apparatus comprising a processor configured toimplement a method recited in any one or more of solutions B1 to B6.

B8. A computer-readable medium having instructions stored thereon, theinstructions, when executed, causing a processor to implement a methodrecited in one or more of solutions B1 to B6.

B9. A computer readable medium that stores the bitstream generatedaccording to any one or more of solutions B1 to B6.

B10. A video processing apparatus for storing a bitstream, wherein thevideo processing apparatus is configured to implement a method recitedin any one or more of solutions B1 to B6.

In the present document, the term “video processing” may refer to videoencoding, video decoding, video compression or video decompression. Forexample, video compression algorithms may be applied during conversionfrom pixel representation of a video to a corresponding bitstreamrepresentation or vice versa. The bitstream representation of a currentvideo block may, for example, correspond to bits that are eitherco-located or spread in different places within the bitstream, as isdefined by the syntax. For example, a macroblock may be encoded in termsof transformed and coded error residual values and also using bits inheaders and other fields in the bitstream. Furthermore, duringconversion, a decoder may parse a bitstream with the knowledge that somefields may be present, or absent, based on the determination, as isdescribed in the above solutions. Similarly, an encoder may determinethat certain syntax fields are or are not to be included and generatethe coded representation accordingly by including or excluding thesyntax fields from the coded representation.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an field programmable gate array (FPGA) or anapplication specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., erasable programmable read-onlymemory (EPROM), electrically erasable programmable read-only memory(EEPROM), and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto optical disks; and compact disc,read-only memory (CD ROM) and digital versatile disc read-only memory(DVD-ROM) disks. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of video processing, comprising:performing a conversion between a video comprising one or more picturesin one or more video layers and a bitstream of the video, wherein thebitstream comprises a coded video sequence that includes an access unit,wherein the bitstream further comprises a first syntax elementindicating whether the access unit includes a first type of picture foreach video layer making up the coded video sequence, wherein the firstsyntax element corresponds to an access unit delimiter networkabstraction layer unit, and wherein the access unit delimiter networkabstraction layer unit is an only access unit delimiter networkabstraction layer unit present in each intra random access point accessunit or gradual decoding refresh access unit when a second syntaxelement, which is indicative of a maximum allowed number of layers ineach coded video sequence that refers to a video parameter set, isgreater than one.
 2. The method of claim 1, wherein the access unitincludes the first type of picture for each video layer; and the accessunit is configured to start a new coded video sequence, or each pictureof the access unit is the first type of picture.
 3. The method of claim1, wherein the first type of picture for each video layer is an intrarandom access point picture or a gradual decoding refresh picture. 4.The method of claim 1, wherein the first syntax element is a flagindicating whether the access unit containing an access unit delimiteris an intra random access point access unit or a gradual decodingrefresh access unit.
 5. The method of claim 1, wherein the second syntaxelement indicates the maximum allowed number of layers by indicating themaximum allowed number minus
 1. 6. The method of claim 1, wherein thefirst syntax element equaling one is indicative of all slices in theaccess unit comprising an identical network abstraction layer unit typein a range of IDR_W_RADL to GDR_NUT, inclusive.
 7. The method of claim6, wherein the first syntax element equaling one and the networkabstraction layer unit type being IDR_W_RADL or IDR_N_LP are indicativeof the access unit being a coded video sequence start access unit. 8.The method of claim 6, wherein a variable for each of the pictures inthe access unit equaling one and the network abstraction layer unit typebeing CRA_NUT or GDR_NUT are indicative of the access unit being a codedvideo sequence start access unit.
 9. The method of claim 8, wherein thevariable indicates whether pictures in a decoded picture buffer prior toa current picture in decoding order are output before the pictures arerecovered.
 10. The method of claim 1, wherein the conversion comprisesdecoding the video from the bitstream.
 11. The method of claim 1,wherein the conversion comprises encoding the video into the bitstream.12. An apparatus for processing video data comprising: a processor; anda non-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toperform a conversion between a video comprising one or more pictures inone or more video layers and a bitstream of the video, wherein thebitstream comprises a coded video sequence that includes an access unit,wherein the bitstream further comprises a first syntax elementindicating whether the access unit includes a first type of picture foreach video layer making up the coded video sequence, wherein the firstsyntax element corresponds to an access unit delimiter networkabstraction layer unit, and wherein the access unit delimiter networkabstraction layer unit is an only access unit delimiter networkabstraction layer unit present in each intra random access point accessunit or gradual decoding refresh access unit when a second syntaxelement, which is indicative of a maximum allowed number of layers ineach coded video sequence that refers to a video parameter set, isgreater than one.
 13. The apparatus of claim 12, wherein the first typeof picture for each video layer is an intra random access point pictureor a gradual decoding refresh picture.
 14. A non-transitorycomputer-readable storage medium storing instructions that cause aprocessor to: perform a conversion between a video comprising one ormore pictures in one or more video layers and a bitstream of the video,wherein the bitstream comprises a coded video sequence that includes anaccess unit, and wherein the bitstream further comprises a first syntaxelement indicating whether the access unit includes a first type ofpicture for each video layer making up the coded video sequence, whereinthe first syntax element corresponds to an access unit delimiter networkabstraction layer unit, and wherein the access unit delimiter networkabstraction layer unit is an only access unit delimiter networkabstraction layer unit present in each intra random access point accessunit or gradual decoding refresh access unit when a second syntaxelement, which is indicative of a maximum allowed number of layers ineach coded video sequence that refers to a video parameter set, isgreater than one.
 15. The non-transitory computer-readable storagemedium of claim 14, wherein the first type of picture for each videolayer is an intra random access point picture or a gradual decodingrefresh picture.
 16. A non-transitory computer-readable recording mediumstoring a bitstream of a video which is generated by a method performedby a video processing apparatus, wherein the method comprises:generating a bitstream of a video comprising one or more pictures in oneor more video layers, wherein the bitstream comprises a coded videosequence that includes an access unit, wherein the bitstream furthercomprises a first syntax element indicating whether the access unitincludes a first type of picture for each video layer making up thecoded video sequence, wherein the first syntax element corresponds to anaccess unit delimiter network abstraction layer unit, and wherein theaccess unit delimiter network abstraction layer unit is an only accessunit delimiter network abstraction layer unit present in each intrarandom access point access unit or gradual decoding refresh access unitwhen a second syntax element, which is indicative of a maximum allowednumber of layers in each coded video sequence that refers to a videoparameter set, is greater than one.
 17. The non-transitorycomputer-readable recording medium of claim 16, wherein the first typeof picture for each video layer is an intra random access point pictureor a gradual decoding refresh picture.